Comment by npodbielski

> With good insulation you can easily store heat for a day which is all you need. You're never going to get close to storing summer heat for the winter. That's not impossible but not feasible for something this scale (and not cost effective at any scale).

This is ground basically. How deep varies but few meters underground you basically have average yearly temperature. You could pump heat from house to the ground to take it out from the ground during winter.